This application is based upon and claims priority from prior French Patent Application No. 98-14136, filed Nov. 10, 1998, the entire disclosure of which is herein incorporated by reference.
1. Field of the Invention
The present invention relates to electronic circuits, and more specifically to a method of controlling an electronic circuit such as the memory of a chip card.
2. Description of Related Art
The control of contactless chip cards, such as bank cards, telephone cards, and the like, is carried out at a distance through an electromagnetic wave, which is generally in the radio frequency spectrum. For this purpose, a control unit is equipped with an antenna and circuitry for generating, modulating, and transmitting a wave of the above-mentioned type in order to transmit data to an antenna at the level of the card. The wave generally has sufficient energy for remotely powering the card""s logic circuits.
The card includes circuitry for transforming the electromagnetic energy received by its antenna into both a regulated voltage supply and binary data that can be exploited by the logic circuits. In response, data can then be sent from the card to the control unit in accordance with the load modulation principle. Such a modulation consists of varying the current consumption at the level of the card""s antenna. This variation creates a perturbation that induces a voltage variation detectable at the antenna of the control unit. The control unit has circuitry for processing and shaping this voltage variation in order to retrieve the data transmitted by the card.
Telephone cards presently in circulation in many countries are equipped with contacts. For their control, they are accessed via metallic pads that come into electrical contact with the terminals of the control unit (or reader). Efforts have been going on for some time to replace existing contact-type telephone cards and their associated readers with equivalent products that can support a contactless type of control, but without having to modify the structure of the logic circuits of the present cards or their basic functioning.
While it is desirable to escape the problems inherent in transmission through contacts (e.g., positioning errors between the reader""s terminals and the pads on the card, wear or oxidation of the terminals and/or the pads, and heat build-up), there is a reluctance to discard the technical consensus regarding the cards themselves that was agreed upon by the various parties (e.g., card manufacturers, card reader manufacturers, and telephone operators). Thus, the problem becomes implementing present data transmission methods based on electromagnetic waves to create a contactless interface between the present types of readers and cards.
The present methods for transmitting data by electronic wave comply with specification standards, such as the xe2x80x9cISO 14443-2 type Bxe2x80x9d standard used in France. These standards particularly define the frequency, power level, types of coding, and electromagnetic transmission spectrum over the transmission channel. In addition, present telephone cards only accept a very small number of commands, of which at least some command words are ill suited for remote control conforming to the abovementioned specifications.
For example, a command to read out from the memory of a telephone card causes two distinct commands to be executed: the incrementation of the card""s address counter, and the readout of data stored in the card""s memory at the address indicated by the current value of the counter (as well as the transmission of that data to the reader). Accordingly, to read the data stored at an address n+m (where n and m are whole numbers and n designates the current value of the address counter), a sequence of m successive readout commands must be executed. This sequence involves the alternating transmission of m command words from the reader to the card and m data words from the card to the reader.
Because of the operating principle of the contactless cards outlined in the introduction, the xe2x80x9cISO 14443-2 type Bxe2x80x9d standard imposes a certain delay between each of these transmissions. The delay allows the control unit to pass over from the transmission mode to the reception mode and vice-versa (this is known as the xe2x80x9cturnaroundxe2x80x9d of the control unit""s antenna). These dead or silent times, during which no data is transmitted in either direction, are on the order of 150 xcexcs (microseconds). It can be understood that executing a command of the type described above in compliance with the xe2x80x9cISO 14443-2 type Bxe2x80x9d specification can cause the average access time to be considerable, and in any case hardly compatible with the speed constraints called for by the application.
A possible solution is to increase the number of commands recognized by the card. For example, two distinguished commands could be provided: one for the address counter incrementation function and another for the data readout and transmission function. Then, to read out the data at address n+m, it would be necessary to transmit the first command m times and the second command just once. Because only the second command requires a turnaround at the control unit""s antenna, and hence a dead time, the average memory access time is reduced. However, it is not possible to make such an increase in the number of commands without an in-depth modification in the structure of the telephone card""s logic circuits. Moreover, increasing the number of distinct commands makes it necessary to increase the size of the binary words that encode these commands (i.e., the command words). In general, there arises a problem in all applications in which the number of distinct commands is limited.
In view of these drawbacks, it is an object of the present invention to overcome the above-mentioned drawbacks and to provide a method of controlling an electronic circuit. The same command is interpreted in a first manner in a first manner if it is followed by a predetermined dead time, and in a second manner if a new command is transmitted before expiration of the predetermined dead time. Thus, it is possible to increase the number of command functions without increasing the number of commands.
One embodiment of the present invention provides a method of controlling an electronic circuit in which a command is received from a control unit. The command is interpreted in either a first manner if the command is followed by a predetermined dead time, or a second manner if a new command is transmitted before expiration of the predetermined dead time. In a preferred embodiment, the command is interpreted in the second manner only if the new command is identical to the command.
Another embodiment of the present invention provides a chip card that includes an antenna, at least one memory, and a control circuit. When a command is received, the control circuit performs either a first function if the command is followed by a predetermined dead time, or a second function if a new command is transmitted before expiration of the predetermined dead time.
Yet another embodiment of the present invention provides a telephone apparatus that includes a read/write device for contactless control of a chip card. The read/write device includes an antenna and a control circuit. When a command is transmitted, the control circuit either allows a predetermined dead time to pass to instruct the chip card to perform a first ftnction, or transmits a new command before expiration of the predetermined dead time to instruct the chip card to perform a second function. In one preferred embodiment, the predetermined dead time is at least as long as a time necessary to transition the read/write device from a transmission mode to a reception mode.
Other objects, features, and advantages of the present invention will become apparent from the following detailed description. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the present invention, are given by way of illustration only and various modifications may naturally be performed without deviating from the present invention.